Regenerative relay system and regenerative relay apparatus

ABSTRACT

A regenerative relay method includes the steps of: i) calculating an error rate of a transmission path between the first half apparatus and a main apparatus; ii) calculating an error rate of a transmission path between the main apparatus and the latter apparatus; iii) adding the error rates; iv) selecting the error correction code and data before the error is corrected in the main apparatus so as to be supplied to the latter apparatus if the added error rates are lower than a designated error correction threshold; and v) selecting data after the error is corrected in the main apparatus and the other error correction code generated from the data so as to be supplied to the latter apparatus if the added error rates are higher than the designated error correction threshold.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a U.S. continuation application filed under 35 USC111(a) claiming benefit under 35 USC 120 and 365(c) of PCT applicationJP2003/009928, filed Aug. 5, 2003. The foregoing applications are herebyincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to regenerative relay methodsand regenerative relay apparatuses, and more specifically, to aregenerative relay method and regenerative relay apparatus whereby, forexample, a regenerative relay of a signal is implemented in an opticaltransmission system such as a Dense Wavelength Division Multiplexer(DWDM) system.

2. Description of the Related Art

Recently and continuing, due to the increase of communicationscapability, a large amount of data can be transmitted by a transmissionapparatus and long distance transmission of data can be done. In thisstate, an efficient optical transmission system using WavelengthDivision Multiplexing is utilized. In this Wavelength Division Multiplextransmission, deterioration of light often happens due to mixing ofnoise by the optical amplifier, light dispersion or polarization by along distance transmission, or the like. Because of this, instead of useof an expensive compensator or low noise amplifier, an error correctionfunction whereby a signal is encoded by adding a redundancy bit and thesignal is decoded at a receiving side, has been used.

An S/N ratio improved by the error correction is generally called acoding gain. Various kinds of error correction have been developeddepending on their coding rules or the number of the redundancy bits.Generally, as the coding gain is larger, that is, the error correctionability is higher, the number of the redundancy bits is bigger, circuitsize is bigger, delay time is longer, and consumption of electric poweris larger.

Transmission capacity has been recently extremely improved so that atransmission capacity of 10 Gbit/s or 40 Gbit/s has been utilized.Therefore, an error correction method wherein the number of theredundancy bits, the circuit size, the delay time, and the consumptionof electric power are respectively small but the coding gain is large indemanded.

In addition, an INVERSE-MUX method has been used. According to thismethod, a signal having a larger capacity is divided into plural routesand transmitted so that the signal is multiplexed at a transmitted sideand the original signal is regenerated. In this method, for example, inorder to divide and transmit a signal having a capacity of 40 Gbit/sinto four routes of 10 Gbit/s each and then multiplex to generate thesignal having a capacity of 40 Gbit/s again, it is necessary to minimizethe differences of the delay times of the transmitted four routes andtherefore the delay time is increased due to the number of the relayapparatuses of the respective routes.

FIG. 1 is a block diagram of an example of a related art transmissionsystem. Referring to FIG. 1, in a terminal apparatus 10, a redundancybit is added to a client signal by using an encoding part 12 so that theclient signal is encoded. The coded signal is converted to an opticalsignal by an electric/optical conversion part 14. The converted opticalsignal is multiplexed by an optical wavelength multiplexer 16 so as tobe sent out to a transmission path at a network side.

The optical multiplex signal that is sent out is optical-level generatedby an optical amplifier (ILA) 17 ₁, 17 ₂, and 17 ₃ arranged on thetransmission path of the network so as to be transmitted. In addition,the signals are divided into individual optical signals by an opticalwavelength divider 18 so as to be transmitted to a regenerative relayapparatus 20.

In the regenerative relay apparatus 20, the signal converted to theelectric signal by the optical/electric conversion part 22 is decoded sothat the error correction is made and the signal is regenerated by thesignal generation part 26. After that, a redundancy bit is added againby an encoding part 28 so that the signal is encoded. The signal isconverted to an optical signal by an electric/optical conversion part30, and then the signal is multiplexed by an optical wavelengthmultiplexer 32 so as to be sent out to the transmission path at thenetwork side. The signal is transmitted to a terminal apparatus 34situated in a remote position by repeating this process. In the terminalapparatus receiving the signal, after the error correction is made, thesignal is used as a transmission signal to the client.

In the meantime, Japan Laid-Open Patent Application Publication No.2000-341344 discloses that a signal converted to an electric signal by alight receiving element is binarized and demultiplexed into n-channelsby a comparator, errors of the binarized signals of respective channelsare corrected by an error correction circuit, a total error numberobtained by counting the number of the errors of the channels issupplied to a threshold value control circuit, the threshold controlcircuit allows a threshold generation circuit to generate pluralthresholds used by the comparator, and an optimum threshold isdetermined on the basis of the total error number.

In the related art transmission system, decoders having constant errorcorrection abilities regardless of the transmission path qualities areprovided in the regenerative relay apparatus and the terminal apparatus.Therefore, the signal passes through the decoder even at a section wherethe number of errors is small so that signal delay by the decoder andthe encoder is increased.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to providea novel and useful regenerative relay method and regenerative relayapparatus.

Another and more specific object of the present invention is to providea regenerative relay method and regenerative relay apparatus whereby anecessary error correction is made without increasing delay time andgood transmission quality can be secured.

The above object of the present invention is achieved by a regenerativerelay method wherein data to which an error correction code is added aretransmitted from a first half apparatus so that an error correction ismade, and another error correction code is generated from the data afterthe error is corrected so as to be transferred to a latter apparatus,the method including the steps of:

calculating an error rate of a transmission path between the first halfapparatus and a main apparatus;

calculating an error rate of a transmission path between the mainapparatus and the latter apparatus;

adding the error rates;

selecting the error correction code and data before the error iscorrected in the main apparatus so as to be supplied to the latterapparatus if the added error rates are lower than a designated errorcorrection threshold; and

selecting data after the error is corrected in the main apparatus andthe other error correction code generated from the data so as to besupplied to the latter apparatus if the added error rates are higherthan the designated error correction threshold.

According to the present invention, it is possible to make a necessaryerror correction without increasing delay time and secure goodtransmission quality.

Other objects, features, and,advantages of the present invention will become more apparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example of a related art transmissionsystem;

FIG. 2 is a structural view of a first embodiment of a relay method ofthe present invention;

FIG. 3 is a view showing an example of a frame format of a transmissionsignal;

FIG. 4 is a view for explaining generation and storage of an errordetecting code BIP8;

FIG. 5 is a structural view of a second embodiment of the relay methodof the present invention;

FIG. 6 is a structural view of a third embodiment of the relay method ofthe present invention;

FIG. 7 is a structural view of a fourth embodiment of the relay methodof the present invention;

FIG. 8 is a structural view of a fifth embodiment of the relay method ofthe present invention;

FIG. 9 is a structural view of a sixth embodiment of the relay method ofthe present invention;

FIG. 10 is a structural view of a seventh embodiment of the relay methodof the present invention;

FIG. 11 is a structural view of an eighth embodiment of the relay methodof the present invention;

FIG. 12 is a structural view of an example of an optical transmissionsystem; and

FIG. 13 is a flowchart of an example of a determination processimplemented by a monitor apparatus 810.

DETAILED DESCRIPTION OF THE PREFERED EMBODIMENTS

A description is given below, with reference to the FIG. 2 through FIG.13 of embodiments of the present invention.

First Embodiment of the Present Invention

FIG. 2 is a structural view of a first embodiment of a relay method ofthe present invention. Referring to FIG. 2, an error correction codethat is a redundancy bit for error correction is added to a signal in anencoding part 41 of a terminal apparatus 40. Overhead is added to thesignal by an OH transmission part 42 so as to be transmitted to aregenerative relay apparatus 44 via a going-up (upstream) circuit.

FIG. 3 is a view showing an example of a frame format of a transmissionsignal. This shows the frame structure of a digital wrapper recommendedby ITU-T G709. The transmission signal has a 4080×4 byte structure. Thisframe structure includes the overhead OH of 56 (=14×4) bytes, a dataarea OPUk of 15296 (=3824×4) bytes, and an error correction code FEC(Forward Error Correction) of 1024 byte.

An error detection code BIP 8 (Bit Interleaved Parity-level 8) is storedin the ninth column of the first line of the overhead. Backward errorinformation BEI (Backward Error Indication) and forward errorinformation (Forward Error Indication) are stored in the tenth column.

Backward correction information BCI (Backward Correction Indication) andforward correction information FCI (Forward Correction Information) arestored in the thirteenth column. Control information CMD is stored inthe fourteenth column.

As shown in FIG. 4, the error detection code BIP 8 stores a parity valuecalculated from a data area (OPUk) of a frame i in the overhead of aframe i+2 which is two frames after the frame i. In addition, an errorcorrection code (FEC) is, for example, a BCH (Bose ChaudhuriHocquengham) code or a Reed Solomon code calculated from data of a dataarea OPUk of the frame i, and is stored in the frame i.

In an OH receiving part 45 of the regenerative relay apparatus 44 shownin FIG. 2, the overhead of a receiving frame is terminated, and errordetection is done by using the error detection code BIP 8 in theoverhead and data of the data area OPUk of the frame preceding by twoframes so as to be supplied to an error count part 46. Furthermore, datain the data area OPUk and the error correction code FEC are supplied toa decoding part 47 and a selection part 49.

The decoding part 47 decodes data by implementing the error correctionof the data of the data area OPUk by using the error correction code FECand implements timing regeneration, waveform shaping, and others. Thedata (corresponding to the data area OPUk) for which the errorcorrection is implemented are encoded again by the encoding part 48 sothat the error correction code FEC is generated, and are then suppliedto the selection part 49.

The error count part 46 calculates an error rate of a transmission pathbetween the terminal apparatus 40 and the regenerative relay apparatus44 from an error detection result supplied from the OH receiving part 45and supplies the error rate to an adder 51. The OH receiving part 52terminates the overhead of the receiving frame of a going-down(downstream) circuit so as to take out the backward error informationBEI in the overhead. The backward error information BEI is an error ratebetween the regenerative relay apparatus 44 and the terminal apparatus54 and supplied to the adder 51.

The adder 51 supplies the total of an error rate of the transmissionpath between the terminal apparatus 40 and the regenerative relayapparatus 44 and the error rate of the transmission path between theregenerative relay apparatus 44 and the terminal apparatus 54 to athreshold determination part 53.

The threshold determination part 53 compares an error correctionthreshold determined by an error correction ability set in advance atthe decoding part 57 of the terminal apparatus 54 and the total errorrate supplied from the adder 51. In a case where the total error ratedoes not exceed the threshold, a signal route is selected by theselection part 49 so that the signal goes to the selection part 49without going through the decoding part 47 and the encoding part 48. Onthe other hand, in a case where the total error rate exceeds thethreshold, a signal route is selected by the selection part 49 so thatthe signal goes to the selection part 49 via the decoding part 47 andthe encoding part 48.

The overhead is added to the error correction code FEC and the data inthe data area OPUk being output by the selection part 49 by an OHtransmission part 50. Then, the data in the data area OPUk and the errorcorrection code FEC are transmitted to the terminal apparatus 54 by thegoing-up (upstream) circuit.

The overhead of the receiving frame is terminated at the OH receivingpart 55 of the terminal apparatus 54. Error detection is done by usingthe error detection code BIP 8 in the overhead and data of the data areaOPUk of the frame preceding by two frames so as to be supplied to anerror count part 56. Furthermore, data in the data area OPUk and theerror correction code FEC are supplied to a decoding part 57.

The decoding part 57 decodes data by implementing the error correctionof the data of the data area OPUk by using the error correction code FECand implements timing regeneration, waveform shaping, and others.

The error count part 56 calculates an error rate of a transmission pathbetween the terminal apparatus 50 and the regenerative relay apparatus44 from an error detection result supplied from the OH receiving part 55and supplies the error rate to an OH transmission part 58. The OHtransmission part 58 stores the error rate supplied from the error countpart 56 in the backward error information BEI in the overhead of thetransmission frame of the going-down (downstream) circuit and transmitsthe error rate to the regenerative relay apparatus 44 via a going-down(downstream) circuit.

Thus, by the threshold determination part 53, the total of the errorrate of the transmission path between the terminal apparatus 40 and theregenerative relay apparatus 44 and the error rate of the transmissionpath between the regenerative relay apparatus 44 and the terminalapparatus 54 is compared with error correction threshold determined bythe error correction ability set in advance at the decoding part 57. Inthe case where the total error rate does not exceed the error correctionthreshold, the signal route is selected by the selection part 49 so thatthe signal goes to the selection part 49 without going through thedecoding part 47 and the encoding part 48. As a result of this, theerror in a transmission section from the terminal apparatus 40 and theterminal apparatus 54 is corrected by the error correction function ofthe terminal apparatuses 40 and 54 so that the signal does not gothrough the decoding part 47 and the coding part 48 of the regenerativerelay apparatus 44. Hence, it is possible to minimize the signal delay.

In the above-discussed first embodiment, the regenerative relayapparatus 44 is connected to the terminal apparatuses 40 and 54.However, the regenerative relay apparatus 44 may be connected to anotherregenerative relay apparatus, instead of the terminal apparatuses 40 and54.

Second Embodiment of the Present Invention

FIG. 5 is a structural view of a second embodiment of the relay methodof the present invention. Referring to FIG. 5, an error correction codethat is a redundancy bit for error correction is added to a signal in anencoding part 141 of a terminal apparatus 140. Overhead is added to thesignal by an OH transmission part 142 so as to be transmitted to aregenerative relay apparatus 144 via a going-up (upstream) circuit.

In an OH receiving part 145 of the regenerative relay apparatus 144, theoverhead of a receiving frame is terminated. Furthermore, data in thedata area OPUk among the transmission signals of the frame format shownin FIG. 3 and the error correction code FEC are supplied to a decodingpart 147 and a selection part 149.

The decoding part 147 decodes data by implementing the error correctionof the data of the data area OPUk by using the error correction code FECand implements timing regeneration, waveform shaping, and others. Atthis time, an error corrected part is supplied to an error correctionamount count part 146. The data (corresponding to the data area OPUk)for which the error correction is implemented are encoded again by theencoding part 148 so that the error correction code AFEC is generated,and are then supplied to the selection part 149.

The error count part 146 calculates the number of bits of the errorcorrected part supplied from the decoding part 147 and supplies thenumber of error correction bit generated at the transmission pathbetween the terminal apparatus 140 and the regenerative relay apparatus144 to an adder 151. The OH receiving part 152 terminates the overheadof the receiving frame of a going-down (downstream) circuit so as totake out the backward error information BCI in the overhead. Thebackward error information BCI is an error rate between the regenerativerelay apparatus 144 and the terminal apparatus 154 and supplied to theadder 151.

The adder 151 supplies the total of the number of error correction bitsof the transmission path between the terminal apparatus 140 and theregenerative relay apparatus 144 and the number of error correction bitsof the transmission path between the regenerative relay apparatus 144and the terminal apparatus 154 to a threshold determination part 153.

The threshold determination part 153 compares an error correctionthreshold determined by an error correction ability set in advance atthe decoding part 157 of the terminal apparatus 154 and the total numberof the error correction bits supplied from the adder 151. In a casewhere the total error rate does not exceed the threshold, a signal routeis selected by the selection part 49 so that the signal goes to theselection part 149 without going through the decoding part 147 and theencoding part 148. On the other hand, in a case where the total errorrate exceeds the threshold, a signal route is selected by the selectionpart 149 so that the signal goes to the selection part 149 via thedecoding part 147 and the encoding part 148.

The overhead is added to the error correction code FEC and the data inthe data area OPUk being output by the selection part 149 by an OHtransmission part 150. Then, the data in the data area OPUk and theerror correction code FEC are transmitted to the terminal apparatus 154by the going-up (upstream) circuit.

The overhead of the receiving frame is terminated at the OH receivingpart 155 of the terminal apparatus 154. Data in the data area OPUk andthe error correction code FEC among transmission signals of the frameformat shown in FIG. 3 are supplied to a decoding part 157.

The decoding part 157 decodes data by implementing the error correctionof the data of the data area OPUk by using the error correction code FECand implements timing regeneration, waveform shaping, and others. Atthis time, the error corrected part is supplied to an error correctionamount count part 156.

The error count part 156 calculates the number of the bits of the errorcorrected part supplied from the decoding part 157 and supplies thenumber of the error correction bits generated at the transmission pathbetween the regenerative relay apparatus 144 and the terminal apparatus154 to an OH transmission part 158. The OH transmission part 158 storesthe number of the error correction bits supplied from the errorcorrection amount count part 156 in the backward error information BCIin the overhead of the transmission frame of the going-down (downstream)circuit and transmits the number of the bits to the terminal apparatusregenerative relay apparatus 144 via a going-down (downstream) circuit.

Thus, by the threshold determination part 153, the total of the errorcorrection amount of the transmission path between the terminalapparatus 140 and the regenerative relay apparatus 144 and the errorcorrection amount of the transmission path between the regenerativerelay apparatus 144 and the terminal apparatus 154 is compared with theerror correction threshold determined by the error correction abilityset in advance at the decoding part 157. In the case where the totalerror correction amount does not exceed the error correction threshold,the signal route is selected by the selection part 149 so that thesignal goes to the selection part 149 without going through the decodingpart 147 and the encoding part 148. As a result of this, the error in atransmission section from the terminal apparatus 140 and the terminalapparatus 154 is corrected by the error correction function of theterminal apparatuses 140 and 154 so that the signal does not go throughthe decoding part 147 and the encoding part 148 of the regenerativerelay apparatus 144. Hence, it is possible to minimize the signal delay.

In the above-discussed second embodiment, the regenerative relayapparatus 144 is connected to the terminal apparatuses 140 and 154.However, the regenerative relay apparatus 144 may be connected toanother regenerative relay apparatus, instead of the terminalapparatuses 140 and 154.

Third Embodiment

FIG. 6 is a structural view of a third embodiment of the relay method ofthe present invention. The difference between the first embodiment andthe third embodiment is that, in the third embodiment, a thresholddetermination part is provided at a latter part terminal apparatus and aresult of determination by the threshold determination part goes back tothe regenerative relay apparatus so that control of the selection partis implemented.

Referring to FIG. 6, an error correction code that is a redundancy bitfor error correction is added to a signal in an encoding part 241 of aterminal apparatus 240. Overhead is added to the signal by an OHtransmission part 242 so as to be transmitted to a regenerative relayapparatus 244 via a going-up (upstream) circuit.

In an OH receiving part 245 of the regenerative relay apparatus 244, theoverhead of a receiving frame shown in FIG. 3 is terminated, and errordetection is done by using the error detection code BIP 8 in theoverhead and data of the data area OPUk of the frame preceding by twoframes so as to be supplied to an error count part 246. Furthermore,data in the data area OPUk and the error correction code FEC aresupplied to a decoding part 247 and a selection part 249.

The decoding part 247 decodes data by implementing the error correctionof the data of the data area OPUk by using the error correction code FECand implements timing regeneration, waveform shaping, and others. Thedata (corresponding to the data area OPUk) for which the errorcorrection is implemented are encoded again by the encoding part 248 sothat the error correction code FEC is generated, and are then suppliedto the selection part 249.

The error count part 246 calculates an error rate of a transmission pathbetween the terminal apparatus 240 and the regenerative relay apparatus244 from an error detection result supplied from the OH receiving part245 and supplies the error rate to an OH transmission part 250.

In the OH receiving part 252, the overhead of the receiving frame of thegoing-down (downstream) circuit is terminated and control informationCMD in the overhead is taken out. The control information CMD is anorder for making the selection part 249 select a signal route withoutgoing through the decoding part 247 and a encoding part 248 or a signalroute going through the decoding part 247 and the encoding part 248. Theselection part 249 follows this order so as to select either one of thesignal routes and supplies the signal to the OH receiving part 250.

The data in the data area OPUk output from the selection part 249 andthe error correction code FEC are supplied to the OH receiving part 250.In the OH receiving part 250, the error rate supplied from the errorcount part 246 is stored in forward error information FEI in theoverhead so that the going-up (upstream) circuit is transmitted to theterminal apparatus 254.

In an OH receiving part 255 of the regenerative relay apparatus 254, theoverhead of a receiving frame is terminated, and error detection is doneby using the error detection code BIP 8 in the overhead and data of thedata area OPUk of the frame preceding by two frames so as to be suppliedto an error count part 256. In addition, data in the data area OPUk andthe error correction code FEC are supplied to a decoding part 257.Furthermore, forward error information FEI (an error rate of thetransmission path between the terminal apparatus 240 and theregenerative relay apparatus 244) in the overhead is taken out andsupplied to an adder 259.

The decoding part 257 decodes data by implementing the error correctionof the data of the data area OPUk by using the error correction code FECand implements timing regeneration, waveform shaping, and others.

The error count part 256 calculates the error rate of a transmissionpath between the terminal apparatus 254 and the regenerative relayapparatus 244 from the error detection result supplied from the OHreceiving part 255 and supplies the error rate to an adder 259.

The adder 259 supplies the total of an error rate of the transmissionpath between the terminal apparatus 240 and the regenerative relayapparatus 244 and an error rate of the transmission path between theterminal apparatus 254 and the regenerative relay apparatus 244, to thethreshold determination part 260.

The threshold determination part 260 compares an error correctionthreshold determined by an error correction ability set in advance atthe decoding part 257 of the terminal apparatus 254 and the total errorrate supplied from the adder 259. In a case where the total error ratedoes not exceed the threshold, a signal route is selected by theselection part 249 so that the signal goes to the selection part 249without going through the decoding part 247 and the encoding part 248.On the other hand, in a case where the total error rate exceeds thethreshold, an order is supplied to the OH receiving part 261, so that asignal route is selected by the selection part 249 and thereby thesignal goes to the selection part 249 via the decoding part 247 and theencoding part 248.

The OH transmission part 261 stores the order supplied from thethreshold determination part 260 in the control information CMD in theoverhead of the transmission frame of the going-down (downstream)circuit and transmits the order to the regenerative relay apparatus 44via a going-down (downstream) circuit.

Thus, in a case where the total of the error rate of the transmissionpath between the terminal apparatus 240 and the regenerative relayapparatus 244 and the error rate of the transmission path between theregenerative relay apparatus 244 and the terminal apparatus 254 does notexceed the error correction threshold, the signal route is selected bythe selection part 249 so that the signal goes to the selection part 249without going through the decoding part 247 and the encoding part 248.As a result of this, the error in a transmission section from theterminal apparatus 240 to the terminal apparatus 254 is corrected by theerror correction function of the terminal apparatuses 240 and 254 sothat the signal does not go through the decoding part 247 and the codingpart 248 of the regenerative relay apparatus 244. Hence, it is possibleto minimize the signal delay.

In the above-discussed third embodiment, the regenerative relayapparatus 244 is connected to the terminal apparatuses 240 and 254.However, the regenerative relay apparatus 244 may be connected toanother regenerative relay apparatus, instead of the terminalapparatuses 240 and 254.

Fourth Embodiment

FIG. 7 is a structural view of a fourth embodiment of the relay methodof the present invention. The difference between the second embodimentand the fourth embodiment is that, in the fourth embodiment, a thresholddetermination part is provided in a latter part terminal apparatus and aresult of determination by the threshold determination part goes back tothe regenerative relay apparatus so that control of the selection partis implemented.

Referring to FIG. 7, an error correction code that is a redundancy bitfor error correction is added to a signal in an encoding part 341 of aterminal apparatus 340. Overhead is added to the signal by an OHtransmission part 342 so as to be transmitted to a regenerative relayapparatus 344 via a going-up (upstream) circuit.

In an OH receiving part 345 of the regenerative relay apparatus 344, theoverhead of a receiving frame is terminated. Furthermore, data in thedata area OPUk among the transmission signals of the frame format shownin FIG. 3 and the error correction code FEC are supplied to a decodingpart 347 and a selection part 349.

The decoding part 347 decodes data by implementing the error correctionof the data of the data area OPUk by using the error correction code FECand implements timing regeneration, waveform shaping, and others. Atthis time, an error corrected part is supplied to an error correctionamount count part 346. The data (corresponding to the data area OPUk)for which the error correction is implemented is encoded again by theencoding part 348 so that the error correction code FEC is generated,and are then supplied to the selection part 349.

The error count part 346 calculates the number of bits of the errorcorrected part supplied from the decoding part 347 and supplies thenumber of error correction bit generated at the transmission pathbetween the terminal apparatus 340 and the regenerative relay apparatus344 to an OH transmission part 350.

In the OH receiving part 352, the overhead of the receiving frame of thegoing-down (downstream) circuit is terminated and control informationCMD in the overhead is taken out. The control information CMD is anorder for making the selection part 349 select a signal route withoutgoing through a decoding part 347 and a encoding part 348 and or asignal route going through the decoding part 347 and the encoding part348. The selection part 349 follows this order so as to select eitherone of the signal routes and supplies the signal to the OH receivingpart 350.

The data in the data area OPUk output from the selection part 349 andthe error correction code FEC are supplied to the OH receiving part 350.In the OH receiving part 350, the error correction bit number suppliedfrom the error correction number count part 346 is stored in forwarderror correction information FEC in the overhead so that the FEC istransmitted to the terminal apparatus 354 via the going-up (upstream)circuit.

The overhead of the receiving frame is terminated at the OH receivingpart 355 of the terminal apparatus 354. Data in the data area OPUk andthe error correction code FEC among transmission signals of the frameformat shown in FIG. 3 are supplied to a decoding part 357. In addition,forward error correction information FCI (the number of correction bitsof the transmission path between the terminal apparatus 340 and theregenerative relay apparatus 344) in the overhead is taken out andsupplied to an adder 359.

The decoding part 357 decodes data by implementing the error correctionof the data of the data area OPUk by using the error correction code FECand implements timing regeneration, waveform shaping, and others. Atthis time, the error corrected part is supplied to an error correctionamount count part 356.

The error count part 356 calculates the number of the bits of the errorcorrected part at the transmission path between the regenerative relayapparatus 344 and the terminal apparatus 354 from the error correctedpart supplied from the OH receiving part 355 and supplies it to theadder 359.

The adder 359 supplies the total of the number of error correction bitsgenerated at the transmission path between the terminal apparatus 340and the regenerative relay apparatus 344 and the number of errorcorrection bits generated at the transmission path between the terminalapparatus 354 and the regenerative relay apparatus 344, to the thresholddetermination part 360.

The threshold determination part 360 compares an error correctionthreshold determined by an error correction ability set in advance atthe decoding part 357 of the terminal apparatus 354 and the total errorrate supplied from the adder 359. In a case where the total error ratedoes not exceed the threshold, a signal route is selected by theselection part 349 so that the signal goes to the selection part 349without going through the decoding part 347 and the encoding part 348.On the other hand, in a case where the total error rate exceeds thethreshold, an order is supplied to the OH receiving part 361, so that asignal route is selected by the selection part 349 and thereby thesignal goes to the selection part 349 via the decoding part 347 and theencoding part 348.

The OH transmission part 361 stores the order supplied from thethreshold determination part 360 in the control information CMD in theoverhead of the transmission frame of the going-down (downstream)circuit and transmits the order to a terminal apparatus regenerativerelay apparatus 344 via a going-down (downstream) circuit.

Thus, in a case where the total of the error correction amount of thetransmission path between the terminal apparatus 340 and theregenerative relay apparatus 344 and the error correction amount of thetransmission path between the regenerative relay apparatus 344 and theterminal apparatus 354 does not exceed the error correction threshold,the signal route is selected by the selection part 349 so that thesignal goes to the selection part 349 without going through the decodingpart 347 and the encoding part 348. As a result of this, the error in atransmission section from the terminal apparatus 340 and the terminalapparatus 354 is corrected by the error correction function of theterminal apparatuses 340 and 354 so that the signal does not go throughthe decoding part 347 and the coding part 348 of the regenerative relayapparatus 344. Hence, it is possible to minimize the signal delay.

In the above-discussed first embodiment, the regenerative relayapparatus 344 is connected to the terminal apparatuses 340 and 354.However, the regenerative relay apparatus 344 may be connected toanother regenerative relay apparatus, instead of the terminalapparatuses 340 and 354.

Fifth Embodiment

FIG. 8 is a structural view of a fifth embodiment of the relay method ofthe present invention. Referring to FIG. 8, an error correction codethat is a redundancy bit for error correction is added to signals inencoding parts 441 and 442 of a terminal apparatus 440. Either one ofthe signals is selected by a selection part 443 and overhead is added tothe selected signal by an OH transmission part 444 so as to betransmitted to a regenerative relay apparatus 450 via a going-up(upstream) circuit.

Here, the encoding parts 441 and 442 implement encoding wherein each hasan error correction ability that is different such that a redundancy bitrate is 3% or 7% (or, 12% or 25%). The error correction ability of theencoding part 442 is greater than the error correction ability of theencoding part 441. A delay time at the time of decoding in the encodingpart 442 is greater than a delay time at the time of decoding in theencoding part 441. In the encoding parts 441 and 442, encoding withdifferent methods such as a Reed Solomon code or a BHC code may beimplemented.

In the OH receiving part 445, the overhead of the receiving frame of thegoing-down (downstream) circuit is terminated and control informationCMD in the overhead is taken out. The control information CMD is anorder for the selection part 443 to select the encoding part 441 or 442.The selection part 443 follows this order so as to select either one ofthe output signal and supplies the selected signal to the OHtransmission part 444.

In an OH receiving part 445 of the regenerative relay apparatus 450, theoverhead of a receiving frame shown in FIG. 3 is terminated, and errordetection is done by using the error detection code BIP 8 in theoverhead and data of the data area OPUk of the frame preceding by twoframes so as to be supplied to an error count part 452. Furthermore,data in the data area OPUk and the error correction code FEC aresupplied to decoding parts 453 and 454.

The decoding parts 453 and 454 implement decoding corresponding to theencoding parts 441 and 442. The decoding parts 453 and 454 decode databy implementing the error correction of the data of the data area OPUkby using the error correction code FEC and implement timingregeneration, waveform shaping, and others.

The data (corresponding to the data area OPUk) for which the errorcorrection is implemented in the decoding parts 453 and 454 are suppliedto the selection part 455. Either one of the data sets is selected andencoded again by the encoding part 458 so that the error correction codeFEC is generated, the overhead is added by the OH transmission part 459,and the frame is transmitted to the terminal apparatus 460.

The error count part 452 calculates an error rate of a transmission pathbetween the terminal apparatus 440 and the regenerative relay apparatus450 from an error detection result supplied from the OH receiving part451 and supplies the error rate to a threshold determination part 456.

The threshold determination part 456 compares an error correctionthreshold determined by an error correction ability set in advance atthe decoding part 453 and the error of the error count part 452. In acase where the error rate does not exceed the threshold, the decodingpart 453 is selected. In a case where the error rate exceeds thethreshold, an order is supplied to the selection part 455 and the OHtransmission part 457, so that the decoding part 454 is selected.

The OH transmission part 457 stores the order supplied from thethreshold determination part 456 in the control information CMD in theoverhead of the transmission frame of the going-down (downstream)circuit and transmits the order to the terminal apparatus 440 via agoing-down (downstream) circuit.

The overhead of the receiving frame is terminated in the OH receivingpart 461 of the terminal apparatus 460 and the data in the data areaOPUk and the error correction code FEC are supplied to the decoding part462. The decoding part 462 decodes the data by implementing the errorcorrection of the data of the data area OPUk by using the errorcorrection code FEC and implement timing regeneration, waveform shaping,and others again. Thus, in a case where the error rate of thetransmission path between the terminal apparatus 440 and theregenerative relay apparatus 450 does not exceed the error correctionthreshold, the decoding part 453 and the encoding part 441 whose delaytime is small are selected by the selecting parts 443 and 455. In a casewhere error rate of the transmission path between the terminal apparatus440 and the regenerative relay apparatus 450 exceeds the errorcorrection threshold, the decoding part 454 and the encoding part 442whose delay time is greater are selected so that it is possible tominimize the signal delay.

In the above-discussed embodiment, the regenerative relay apparatus 450is connected to the terminal apparatuses 440 and 460. However, theregenerative relay apparatus 450 may be connected to anotherregenerative relay apparatus, instead of the terminal apparatuses 440and 460.

Sixth Embodiment

FIG. 9 is a structural view of a sixth embodiment of the relay method ofthe present invention. Referring to FIG. 9, an error correction codethat is a redundancy bit for error correction is added to signals inencoding parts 541 and 542 of a terminal apparatus 540. Either one ofthe signals is selected by a selection part 543 and overhead is added tothe selected signal by an OH transmission part 544 so as to betransmitted to a regenerative relay apparatus 550 via a going-up(upstream) circuit.

Here, the encoding parts 541 and 542 implement encoding wherein each hasan error correction ability that is different such that a redundancy bitrate is 3% or 7% (or, 12% or 25%). The error correction ability of theencoding part 542 is greater than the error correction ability of theencoding part 541. A delay time at the time of decoding in the encodingpart 542 is greater than a delay time at the time of decoding in theencoding part 541. In the encoding parts 541 and 542, encoding withdifferent methods such as a Reed Solomon code or a BHC code may beimplemented.

In the OH receiving part 545, the overhead of the receiving frame of thegoing-down (downstream) circuit is terminated and control informationCMD in the overhead is taken out. The control information CMD is anorder for the selection part 543 to select the encoding part 541 or 542.The selection part 543 follows this order so as to select either one ofthe output signal and supplies the selected signal to the OHtransmission part 544.

In an OH receiving part 545 of the regenerative relay apparatus 550, theoverhead of a receiving frame shown in FIG. 3 is terminated, and data inthe data area OPUk and the error correction code FEC are supplied todecoding parts 553 and 554.

The decoding parts 553 and 554 implements decoding corresponding to theencoding parts 541 and 542. The decoding parts 553 and 554 decode databy implementing the error correction of the data of the data area OPUkby using the error correction code FEC and implement timingregeneration, waveform shaping, and others. The error corrected parts ofthe decoding parts 553 and 554 are supplied to the selection part 556.Either one of the error corrected parts is selected and supplied to theerror correction amount count part 557.

The data (corresponding to the data area OPUk) for which the errorcorrection is implemented in the decoding parts 553 and 554 are suppliedto the selection part 555. Either one of the data sets is selected andencoded again by the encoding part 560 so that the error correction codeFEC is generated, the overhead is added by the OH transmission part 561,and the frame is transmitted to the terminal apparatus 570.

The error correction amount count part 557 calculates the number of bitsof the error corrected part supplied from the selection part 556, andsupplies the number of error correction bits generated at thetransmission path between the terminal apparatus 540 and theregenerative relay apparatus 550 to a threshold determination part 558.

The threshold determination part 558 compares an error correctionthreshold determined by an error correction ability set in advance atthe decoding part 553 and the error of the error correction amount countpart 557. In a case where the error rate does not exceed the threshold,the decoding part 553 is selected. In a case where the error rateexceeds the threshold, an order is supplied to the selection parts 555and 556 and the OH transmission part 559, so that the decoding part 554is selected.

The OH transmission part 559 stores the order supplied from thethreshold determination part 558 in the control information CMD in theoverhead of the transmission frame of the going-down (downstream)circuit and transmits the order to the terminal apparatus 540 via agoing-down (downstream) circuit.

The overhead of the receiving frame is terminated in the OH receivingpart 571 of the terminal apparatus 570 and the data in the data areaOPUk and the error correction code FEC are supplied to the decoding part572. The decoding part 572 decodes data by implementing the errorcorrection of the data of the data area OPUk by using the errorcorrection code FEC and implements timing regeneration, waveformshaping, and others again.

Thus, in a case where the error rate of the transmission path betweenthe terminal apparatus 540 and the regenerative relay apparatus 550 doesnot exceed the error correction threshold, the decoding part 553 and theencoding part 541 whose delay time is small are selected by theselecting parts 543, 555 and 556. In a case where error rate of thetransmission path between the terminal apparatus 540 and theregenerative relay apparatus 550 exceeds the error correction threshold,the decoding part 554 and the encoding part 542 whose delay time isgreater are selected so that it is possible to minimize the signaldelay.

In the above-discussed embodiment, the regenerative relay apparatus 550is connected to the terminal apparatuses 540 and 570. However, theregenerative relay apparatus 550 may be connected to another regeerativerelay apparatus, instead of the terminal apparatuses 540 and 570.

Seventh Embodiment

FIG. 10 is a structural view of a seventh embodiment of the relay methodof the present invention. The difference between the fifth and seventhembodiments is that, in the seventh embodiment, the thresholddetermination part is provided in a terminal apparatus, too.

Referring to FIG. 10, an error correction code that is a redundancy bitfor error correction is added to signals in encoding parts 641 and 642of a terminal apparatus 640. Either one of the signals is selected by aselection part 643 and an overhead is added to the selected signal by anOH transmission part 644 so as to be transmitted to a regenerative relayapparatus 650 via a going-up (upstream) circuit.

Here, the encoding parts 641 and 642 implement encoding wherein an errorcorrection capability is different for each such that a redundancy bitrate is 3% or 7% (or, 12% or 25%). The error correction ability of theencoding part 642 is greater than the error correction ability of theencoding part 641. A delay time at the time of decoding in the encodingpart. 642 is greater than a delay time at the time of decoding in theencoding part 641. In the encoding parts 641 and 642, encoding systemwhose methods are different such as a Reed Solomon code or a BHC codemay be implemented.

The OH receiving part 645 terminates the overhead of the receiving frameof a going-down (downstream) circuit so as to take out the backwarderror information BEI in the overhead and supply the BEI to thethreshold determination part 646. The backward error information BEI isan error rate between the regenerative relay apparatus 650 and theterminal apparatus 640.

The threshold determination part 646 compares an error correctionthreshold determined by an error correction ability set in advance atthe decoding part 653 and the error rate. In a case where the error-ratedoes not exceed the threshold, the encoding part 641 is selected by theselection part 643. On the other hand, in a case where the error rateexceeds the threshold, the encoding part 642 is selected by theselection part 643.

In an OH receiving part 651 of the regenerative relay apparatus 650, theoverhead of a receiving frame shown in FIG. 3 is terminated, and errordetection is done by using the error detection code BIP 8 in theoverhead and data of the data area OPUk of the frame preceding by twoframes so as to be supplied to an error count part 652. Furthermore,data in the data area OPUk and the error correction code FEC aresupplied to decoding parts 653 and 654.

The decoding parts 653 and 654 implement decoding corresponding to theencoding parts 651 and 642. The decoding parts 653 and 654 decode databy implementing the error correction of the data of the data area OPUkby using the error correction code FEC and implement timingregeneration, waveform shaping, and others. The data (corresponding tothe data area OPUk) for which the error correction is implemented in thedecoding parts 653 and 654 are supplied to the selection part 655.Either one of the data sets is selected and encoded again by theencoding part 658 so that the error correction code FEC is generated,the overhead is added by the OH transmission part 659, and the frame istransmitted to the terminal apparatus 660.

The error count part 652 calculates an error rate of a transmission pathbetween the terminal apparatus 640 and the regenerative relay apparatus650 from an error detection result supplied from the OH receiving part651 and supplies the error rate to a threshold determination part 656and the OH receiving part 657.

The threshold determination part 656 compares an error correctionthreshold determined by an error correction ability set in advance atthe decoding part 653 and the error of the error count part 652. In acase where the error rate does not exceed the threshold, the decodingpart 653 is selected. In a case where the error rate exceeds thethreshold, an order is supplied to the selection part 655, so that thedecoding part 654 is selected.

The OH transmission part 657 stores an error rate supplied from thethreshold determination part 656 in the backward error information BEIin the overhead of the transmission frame of the going-down (downstream)circuit and transmits the error rate to a terminal apparatusregenerative relay apparatus 640 via a going-down (downstream) circuit.

The overhead of the receiving frame is terminated in the OH receivingpart 661 of the terminal apparatus 660 and the data in the data areaOPUk and the error correction code FEC are supplied to the decoding part662. The decoding part 662 decodes data by implementing the errorcorrection of the data of the data area OPUk by using the errorcorrection code FEC and implements timing regeneration, waveformshaping, and others again.

Thus, in a case where the error rate of the transmission path betweenthe terminal apparatus 640 and the regenerative relay apparatus 650 doesnot exceed the error correction threshold, the decoding part 653 and theencoding part 641 whose delay time is small are selected by theselecting parts 643 and 655. In a case where error rate of thetransmission path between the terminal apparatus 640 and theregenerative relay apparatus 650 exceeds the error correction threshold,the decoding part 654 and the encoding part 642 whose delay time isgreater are selected so that it is possible to minimize the signaldelay.

In the above-discussed embodiment, the regenerative relay apparatus 650is connected to the terminal apparatuses 640 and 660. However, theregenerative relay apparatus 650 may be connected to anotherregenerative relay apparatus, instead of the terminal apparatuses 640and 660.

Eighth Embodiment

FIG. 11 is a structural view of an eighth embodiment of the relay methodof the present invention. The difference between the sixth and eighthembodiments is that, in the eighth embodiment, the thresholddetermination part is provided in a terminal apparatus, too. Referringto FIG. 11, an error correction code that is a redundancy bit for errorcorrection is added to signals in encoding parts 741 and 742 of aterminal apparatus 740. Either one of the signals is selected by aselection part 743 and overhead is added to the selected signal by an OHtransmission part 744 so as to be transmitted to a regenerative relayapparatus 750 via a going-up (upstream) circuit.

Here, the encoding parts 741 and 742 implement encoding wherein an errorcorrection capability is different for each such that a redundancy bitrate is 3% or 7% (or, 12% or 25%). The error correction ability of theencoding part 742 is greater than the error correction ability of theencoding part 741. A delay time at the time of decoding in the encodingpart 742 is greater than a delay time at the time of decoding in theencoding part 741. In the encoding parts 741 and 742, encoding systemwith different methods such as a Reed Solomon code or a BHC code may beimplemented.

In the OH receiving part 745, the overhead of the receiving frame of thegoing-down (downstream) circuit is terminated and the backward errorcorrection information BCI in the overhead is taken out. The backwarderror correction information BCI is the number of the error correctionbits at the transmission path between the regenerative relay apparatus750 and the terminal apparatus 740. The threshold determination part 746compares an error correction threshold determined by an error correctionability set in advance at the decoding part 753 and the number of theerror correction bits. In a case where the number of the errorcorrection bits does not exceed the threshold, the encoding part 741 isselected by the selection part 743. On the other hand, in a case wherethe number of the error correction bits exceeds the threshold, thecoding part 742 is selected by the selection part 743.

In an OH receiving part 751 of the regenerative relay apparatus 750, theoverhead of a receiving frame shown in FIG. 3 is terminated, and data inthe data area OPUk and the error correction code FEC are supplied todecoding parts 753 and 754.

The decoding parts 753 and 754 implement decoding corresponding to theencoding parts 741 and 742. The decoding parts 753 and 754 decode databy implementing the error correction of the data of the data area OPUkby using the error correction code FEC and implement timingregeneration, waveform shaping, and others. The error corrected parts ofthe decoding parts 753 and 754 are supplied to the selection part 756.Either one of the error corrected parts is selected and supplied to theerror correction amount count part 757.

The data (corresponding to the data area OPUk) for which the errorcorrection is implemented in the decoding parts 753 and 754 are suppliedto the selection part 755. Either one of the data sets is selected andencoded again by the encoding part 760 so that the error correction codeFEC is generated, the overhead is added by the OH transmission part 761,and the frame is transmitted to the terminal apparatus 770.

The error correction amount count part 757 calculates the number of bitsof the error corrected part supplied from the selection part 756, andsupplies the number of error correction bit generated at thetransmission path between the terminal apparatus 740 and theregenerative relay apparatus 750 to the threshold determination part758.

The threshold determination part 758 compares an error correctionthreshold determined by an error correction capability set in advance atthe decoding part 753 and the error of the error correction amount countpart 757. In a case where the error rate does not exceed the threshold,the decoding part 753 is selected. In a case where the error rateexceeds the threshold, an order is supplied to the selection parts 755and 756 and the OH transmission part 759, so that the decoding part 754is selected.

In the OH transmission part 759, the number of the error correction bitssupplied from the error correction amount count part 757 is stored inthe backward error correction information BCI in the overhead of thetransmission frame of the going-down (downstream) circuit so as to betransmitted to the terminal apparatus 740 via a going-down (downstream)circuit.

The overhead of the receiving frame is terminated in the OH receivingpart 771 of the terminal apparatus 770 and the data in the data areaOPUk and the error correction code FEC are supplied to the decoding part772. The decoding part 772 decodes data by implementing the errorcorrection of the data of the data area OPUk by using the errorcorrection code FEC and implements timing regeneration, waveformshaping, and others again.

Thus, in a case where the error rate of the transmission path betweenthe terminal apparatus 740 and the regenerative relay apparatus 750 doesnot exceed the error correction threshold, the decoding part 753 and theencoding part 741 whose delay time is small are selected by theselecting parts 743, 755 and 756. In a case where error rate of thetransmission path between the terminal apparatus 740 and theregenerative relay apparatus 750 exceeds the error correction threshold,the decoding part 754 and the coding part 742 whose delay time is greatare selected so that it is possible to minimize the signal delay.

In the above-discussed embodiment, the regenerative relay apparatus 750is connected to the terminal apparatuses 740 and 770. However, theregenerative relay apparatus 750 may be connected to anotherregenerative relay apparatus, instead of the terminal apparatuses 740and 770.

Here, as shown in FIG. 12, in order to reduce the delay time in theoptical transmission system where plural regenerative relay apparatuses802, 803, 804, and 805 are made in a cascade connection between theterminal apparatuses 800 and 801, it is necessary to not only apply thefirst through fourth embodiments but also determine which section thesignal does not pass through by using a monitor apparatus 810.

In a case where encoding and decoding are implemented in all of theregenerative relay apparatuses 802, 803, 804 and 805, the delay time ofthe section A between the terminal apparatus 800 and the regenerativerelay apparatus 802 is regarded as τ; the error rate of the section Bbetween the regenerative apparatuses 802 and 803 is regarded as α; theerror rate of the section C between the regenerative apparatuses 803 and804 is regarded as 2α; the error rate of the section D between theregenerative apparatuses 804 and 805 is regarded as 2α; the error rateof the section E between the regenerative apparatus 805 and the terminalapparatus 801 is regarded as α; and an error correction thresholddetermined by the monitor apparatus 810 is regarded as 3α.

FIG. 13 is a flowchart of an example of a determination processimplemented by the monitor apparatus 810. In FIG. 13, error rates at allof the sections of the route are measured in step S10.

Next, in step S12, a section I where the error rate is highest isdetermined. In a case where the error rates are the same, a section nearthe terminal apparatus 800 is selected, for example. In step S14, asection J is determined. The error rate of the section J is highest intwo sections neighboring to the section I whose error rate is determinedto be highest in step S14. In step S16, the error rates of the section Iand Section J are added. In step S18, whether a sum of the error ratesexceeds the error correction threshold (3α) is determined.

In a case where the sum of the error rates is lower than the errorcorrection threshold, in step S20, the section I and section J (or thesection K) are made to be a single section so that the signal does notpass through the section I and section J of the regenerative relayapparatus and the process goes to step S14.

On the other hand, if the sum of the error rates exceeds the errorcorrection threshold, the process goes to step S22 so that whether thesum of the error rates exceeds the threshold twice consecutivelyaccording to the determination in step S18 is determined. If the sum ofthe error rates exceed the threshold only one time, the process goes tostep S24 so that a section K is determined. The error rate of thesection K is low in the two sections neighboring to the section I. Instep S26, the error rates of the section I and the section K are addedand the process returns to step S18 so that whether the sum of the errorrates exceed the error correction threshold (3α) is determined.

Whether the sum of the error rates exceeds the threshold twiceconsecutively is determined in step S22, the section J and the section Kneighboring to the section I cannot be made into a single section.Hence, in step S28 the route is divided into two routes in a state wherethe section I is the boundary and the process returns to step S10 sothat the process after step 10 is repeated for the divided routes.

If the determination process shown in FIG. 13 is not implemented suchthat the error correction threshold is determined from a side of theterminal apparatus 800 in turn, the section A and section B are madesingle so as to be a new section (the error rate of the new section is2α) so that encoding and decoding in the regenerative relay apparatus802 are stopped. Hence, four error correction sections (A+B, C, D, andE) are required.

On the other hand, if the determination process shown in FIG. 13 isimplemented, the section B and section C are made single and the sectionD and section E are made single. Only three error correction sections(A, B+C and D+E) are required so that the delay time can be efficientlyreduced.

According to the above-discussed embodiment of the present invention, itis possible to form a network wherein transmission delay is small sothat the error correction ability based on compositing and decoding canbe used to the maximum. In addition, by reducing the difference of thedelay time between the routes, it is possible to reduce the amount ofmemory necessary for eliminating a phase difference between the routesin the INVERSE-MUX method wherein signals having large capacities aredivided into and transmitted by plural routes and at a part after thesignals are transmitted, the signals are multiplexed so that theoriginal signal is regenerated.

The present invention is not limited to these embodiments, butvariations and modifications may be made without departing from thescope of the present invention.

For example, in the above-discussed embodiments, the error rate iscompared with the error correction threshold. Instead of the error rate,the error correction amount may be compared with the error correctionthreshold.

Either of the first through fourth embodiments may be combined with theeither of the fifth through eighth embodiments. The present invention isnot limited to this. The decoding part 47, 147, 257, 357, 453, 454, 553,554, 653, 654, 753, or 754 corresponds to a decoding part mentioned inthe following claims. The encoding part 48, 148, 641 or 642 correspondsto an encoding part mentioned in the following claims. The error countpart 46, 256, 452 or 652 corresponds to an error count part mentioned inthe following claims. The OH receiving part 52, 152, 255, or 355corresponds to a transfer part mentioned in the following claims. Theadder 51, 151, 259 or 359 corresponds to an adding part mentioned in thefollowing claims. The threshold determination part 53, 153 or 260 or thesection part 49, 149, 455, or 555 corresponds to a selection partmentioned in the followings claims. The error correction amount countpart 146, 356, 557 or 757 corresponds to an error correction amountcount part mentioned in the following claims. The thresholddetermination part 260, 360, 456, or 558 or the OH transmitting part261, 361, 457, or 559 corresponds to a selection order part mentioned inthe following claims. The threshold determination part 656 or 758 or theselection part 655, 755 or 756 corresponds to a comparison selectionpart mentioned in the following claims. The OH transmitting part 657 or759 corresponds to a notification part.

1. A regenerative relay method wherein data to which an error correctioncode is added are transmitted from a first half apparatus so that anerror correction is made, and another error correction code is generatedfrom the data after the error is corrected so as to be transferred to alatter apparatus, the method comprising the steps of: calculating anerror rate of a transmission path between the first half apparatus and amain apparatus; calculating an error rate of a transmission path betweenthe main apparatus and the latter apparatus; adding the error rates;selecting the error correction code and data before the error iscorrected in the main apparatus so as to be supplied to the latterapparatus if the added error rates are lower than a designated errorcorrection threshold; and selecting data after the error is corrected inthe main apparatus and the other error correction code generated fromthe data so as to be supplied to the latter apparatus if the added errorrates are higher than the designated error correction threshold.
 2. Aregenerative relay method wherein data to which an error correction codeis added are transmitted from a first half apparatus so that an errorcorrection is made, and another error correction code is generated fromthe data after the error is corrected so as to be transferred to alatter apparatus, the method comprising the steps of: calculating anerror correction amount of a transmission path between the first halfapparatus and a main apparatus; calculating an error correction amountof a transmission path between the main apparatus and the latterapparatus; adding the error correction amounts; selecting the errorcorrection code and data before the error is corrected in the mainapparatus so as to be supplied to the latter apparatus if the addederror correction amounts are lower than a designated error correctionthreshold; and selecting data after the error is corrected in the mainapparatus and the other error correction code generated from the data soas to be supplied to the latter apparatus if the added error correctionamounts are higher than the designated error correction threshold.
 3. Aregenerative relay apparatus, comprising: a decoding part configured tomake an error correction of data by using an error correction code; anencoding part configured to generate another error correction code fromdata after the error is corrected; an error count part configured tocount an error rate before the error is corrected; a transfer partconfigured to transfer the error rate before the error is corrected froma latter apparatus; an adding part configured to add the error rate inthe regenerative relay apparatus and an error rate reported from thelatter apparatus by a notifying part; and a selection part configured toselect the error correction code and data before the error is correctedin the regenerative relay apparatus so as to be supplied to the latterapparatus if the added error rates are lower than a designated errorcorrection threshold, and configured to select data after the error iscorrected in the regenerative relay apparatus and the other errorcorrection code generated from the data so as to be supplied to thelatter apparatus if the added error rates are higher than the designatederror correction threshold.
 4. A regenerative relay apparatus,comprising: a decoding part configured to make an error correction ofdata by using an error correction code; an encoding part configured togenerate another error correction code from data after the error iscorrected; an error correction amount count part configured to count anamount of an error corrected by the decoding part; a transfer partconfigured to transfer another error correction amount from a latterapparatus; an adding part configured to add the error correction amountin the regenerative relay apparatus and the other error correctionamount reported from the latter apparatus by a notifying part; and aselection part configured to select the error correction code and databefore the error is corrected in the regenerative relay apparatus so asto be supplied to the latter apparatus if the added error correctionamounts are lower than a designated error correction threshold, andconfigured to select data after the error is corrected in theregenerative relay apparatus and the other error correction codegenerated from the data so as to be supplied to the latter apparatus ifthe added error correction amounts are higher than the designated errorcorrection threshold.
 5. A regenerative relay apparatus, comprising: adecoding part configured to make an error correction of data by using anerror correction code; an error count part configured to count an errorrate before the error is corrected; a transfer part configured totransfer the error rate before the error is corrected from a first halfapparatus; an adding part configured to add the error rate in theregenerative relay apparatus and another error rate reported from thefirst half apparatus by a notifying part; and a selection order partconfigured to make the first half apparatus select an error correctioncode and data before the error is corrected in the regenerative relayapparatus so as to be supplied to the regenerative relay apparatus ifthe added error rates are lower than a designated error correctionthreshold, and configured to make the first half apparatus select dataafter the error is corrected in the regenerative relay apparatus and anerror correction code generated from the data so as to be supplied tothe regenerative relay apparatus if the added error rates are higherthan a designated error correction threshold.
 6. A regenerative relayapparatus, comprising: a decoding part configured to make an errorcorrection of data by using an error correction code; an errorcorrection amount count part configured to count an amount of an errorcorrected by the decoding part; a transfer part configured to transferanother error correction amount from a first half apparatus; an addingpart configured to add the error correction amount in the regenerativerelay apparatus and the other error correction amount reported from thefirst half apparatus by a notifying part; and a selection partconfigured to make a selection in the first half apparatus of the errorcorrection code and data before the error is corrected in theregenerative relay apparatus so as to be supplied to the regenerativerelay apparatus if the added error correction amounts are lower than adesignated error correction threshold, and configured to make the firsthalf apparatus select data after the error is corrected in theregenerative relay apparatus and another error correction code generatedfrom the data so as to be supplied to the regenerative relay apparatusif the added error correction amounts are higher than the designatederror correction threshold.
 7. A regenerative relay method wherein datato which an error correction code is added are transmitted from a firsthalf apparatus so that an error correction is made, and another errorcorrection code is generated from the data after the error is correctedso as to be transferred to a latter apparatus, the method comprising thesteps of: calculating an error rate of a transmission path between thefirst half apparatus and a main apparatus; selecting and encoding anerror correction code having a low correction rate in the first halfapparatus and selecting and decoding an error correction code having alow correction rate in the main apparatus if the error rate is lowerthan a designated error correction threshold; and selecting and encodingan error correction code having a high correction rate in the first halfapparatus and selecting and decoding an error correction code having ahigh correction rate in the main apparatus if the error rate is higherthan the designated error correction threshold.
 8. A regenerative relaymethod wherein data to which an error correction code is added aretransmitted from a first half apparatus so that an error correction ismade, and another error correction code is generated from the data afterthe error is corrected so as to be transferred to a latter apparatus,the method comprising the steps of: calculating an error rate of atransmission path between the first half apparatus and a main apparatus;selecting and encoding an error correction code having a low correctionrate in the first half apparatus and selecting and decoding an errorcorrection code having a low correction rate in the main apparatus ifthe error correction amount is lower than a designated error correctionthreshold; and selecting and coding an error correction code having ahigh correction rate in the first half apparatus and selecting anddecoding an error correction code having a high correction rate in themain apparatus if the error correction amount is higher than thedesignated error correction threshold.
 9. A regenerative relayapparatus, comprising: a plurality of decoding parts configured to makeerror correction of data, each of the decoding parts having a differentcorrection rate; an error count part configured to count an error ratebefore the error is corrected; a selection part configured to select oneof the plural decoding parts based on a result of comparison between theerror rate and a designated error correction threshold; and a selectionorder part configured to order a first half apparatus to select one ofthe plural decoding parts having different correction rates,corresponding to the selection of the one of the decoding part.
 10. Aregenerative relay apparatus, comprising: a plurality of decoding parts,each of the decoding parts being configured to make error correction ofdata and having a different correction rate; an error correction amountcount part configured to count an amount of an error corrected by thedecoding part selected from the plural decoding parts by a selectionpart; the selection part configured to select one of the plural decodingparts based on a result of comparison between the error correctionamount and a designated error correction threshold; and a selectionorder part configured to order a first half apparatus to select one ofthe plural decoding parts having different correction rates,corresponding to a selection of the one of the decoding parts.
 11. Aregenerative relay apparatus, comprising: a plurality of decoding parts,each decoding part being configured to make error correction of data andhaving a different correction rate; an error count part configured tocount an error rate before the error is corrected; and a notificationpart configured to communicate the error rate to a first half apparatus;wherein the error rate communicated by the notification part is comparedwith a designated error correction threshold so that one of a pluralityof decoding parts of the first half apparatus is selected.
 12. Aregenerative relay apparatus, comprising: a plurality of decoding parts,each of the decoding parts being configured to make error correction ofdata and having a different correction rate; an error correction amountcount part configured to count an amount of an error corrected by one ofthe decoding parts selected from the plural decoding parts by acomparison selection part; the comparison selection part configured toselect the one of the plural decoding parts based on a result ofcomparison between the error correction amount and a designated errorcorrection threshold; and a notification part configured to communicatethe error correction amount to a first half apparatus; wherein the errorcorrection amount communicated from the notification part is comparedwith the designated error correction threshold so that one of aplurality of decoding parts of a first half apparatus is selected.
 13. Aregenerative relay method of a transmission system wherein a pluralityof regenerative relay apparatuses are made cascade-connected, each ofthe regenerative relay apparatuses comprising: a decoding partconfigured to make an error correction of data by using an errorcorrection code; an encoding part configured to generate another errorcorrection code from data after the error is corrected; an error countpart configured to count an error rate before the error is corrected; atransfer part configured to transfer the error rate before the error iscorrected from a latter apparatus; an adding part configured to add theerror rate in the regenerative relay apparatus and another error ratecommunicated from the latter apparatus by a notifying part; and aselection part configured to select the error correction code and databefore the error is corrected in the regenerative relay apparatus so asto be supplied to the latter apparatus if the added error rates arelower than a designated error correction threshold, and configured toselect data after the error is corrected in the regenerative relayapparatus and the other error correction code generated from the data soas to be supplied to the latter apparatus if the added error rates arehigher than the designated error correction threshold; the regenerativerelay method comprising the steps of: calculating an error rate betweenthe neighboring regenerative relay apparatuses; and adding an error rateof a section whose error rate is highest and an error rate of a sectionneighboring the section whose error rate is highest; wherein the sectionwhose error rate is highest and the other neighboring section are madesingle and decoding and encoding in the regenerative relay apparatus arestopped, if the added error rates are equal to or less than the errorcorrection threshold.